Six attacks on state-owned Pemex pipelines in Mexico, including in Omealca, above, caused a 25 percent drop in the natural gas supply nationwide.

MALTRATA, Mexico – A leftist guerrilla group claimed credit Tuesday for the bombing attacks a day earlier of six Pemex pipelines in central Mexico, as officials conceded it was impossible for police and army troops to protect the company’s vast fuel-distribution network.

The Revolutionary Popular Army (known by the acronym EPR in Spanish) said 12 of its “military units” had undertaken the attacks in Veracruz and Tlaxcala states to force the government to hand over two EPR militants who disappeared earlier this year.

The EPR says they were arrested by authorities in Oaxaca, but officials there deny they detained the men.

On Tuesday, Pemex officials said the attacks had caused a 25 percent drop in the supply of natural gas available to consumers across Mexico. Several factories remained closed for lack of fuel, including the Volkswagen plant in Puebla.

Fires set off at the bombed pipelines largely were contained Tuesday. But Pemex officials said it may take days to repair the severed lines. The attacks caused natural gas shortages in at least 10 states.

Coming two months after similar attacks in Guanajuato and Queretaro, the bombings also were a blow to the government of Felipe Calderón, who has made security a centerpiece of his presidency.

In Maltrata, a town of 14,000 in Veracruz state, most residents returned home a day after the EPR bombed a nearby concrete Pemex structure. The small building, less than a mile outside the town limits, contained a valve station linked to three lines that carried gasoline and natural gas.

The town sits in a small valley and many residents fled to the surrounding hillsides in the midst of a heavy rainstorm.

“At about 2 a.m., the ground shook, and we heard a thunderclap,” said resident Genaro Marcelino, recalling the bombing. “We grabbed what we could, ran out of the house and into the hills. It was raining cats and dogs. We saw the sky light up.”

Authorities said no one was injured in the blasts.

Officials said the method employed in the attack was similar to bombings for which EPR claimed responsibility in July. Monday’s devices used shaped plastic explosives, known as “sausage” bombs, and were detonated remotely by cell phones.

On Monday, one bomb was discovered intact, with a message attached. “Alive you took them, alive we want them back,” the note read, in an apparent reference to missing EPR militants.

Local news reported that army troops briefly had been posted to the Maltrata pipelines after the July attacks, but had been removed. An army bomb squad surveyed several miles of the line near Maltrata after an anonymous threat on July 18 but declared the incident a “false alarm.”

Pemex general director Jesus Reyes Heroles said Tuesday the state-owned distribution network, which includes 30,000 miles of pipelines, was simply too large to guard completely.